Micrometer operating mechanism



June 22, 1965 F. G. ZAGAR 3,190,009

MICROMETER OPERATING MECHANISM Filed April 26, 1962 3 Sheets-Sheet l FlG.l

INVENTOR.

FRANK G. ZAGAR BY I ATTORNEYS June 22, 1965 F. G. ZAGAR 3,190,009

MICROMETER OPERATING MECHANISM Filed April 26, 1962 s Sheets-Sheet 2 INVENTOR. FRANK G] ZAGAR 3 BY W F? N EYS June 22, 1965 F. G. ZAGAR 3,190,009

7 MICROMETER OPERATING MECHANISM Filed April 26, 1962 5 Sheets-Sheet 3 5 1 M m ifi ig ,1 H

H l H I I I' I III INVENTOR. r J I FRANK G. ZAGAR ATTORNEYS United States Patent 3,190,009 MICROMETER OPERATING MECHANISM Frank G. Zagar, Euclid, Ohio, assignor to Zagar, Inc., a corporation of Ohio Filed Apr. 26, 1962, Ser. No. 190,469 12 Claims. (Cl. 33- 166) My invention relates to mechanisms for operating micrometers and for indicating the position of the same.

An object of the invention is to provide improved means for driving a micrometer to operate the same.

Another object is the provision for readily and accu- Iately determining the position of a micrometer barrel or head in the measuring of parts and to readily rotate the head or barrel from a power source.

Another object is the provision of improved apparatus for obtaining a proportional drive for a rotatable micrometer head or barrel and for determining the relative position of the head or barrel by a determination of the rotational progress of an electric motor powering the proportional drive.

Another object is the provision of an improved mechanism for rotating a micrometer head or barrel by an electric motor, for providing a fixed ratio between the rotation of the motor rotor and the rotation of the micrometer head or barrel and for a determination of the rotational progress of the motor rotor and thus an indication of the proportional progress of rotation of the micrometer head or barrel.

Another object is the provision of improved apparatus for operating a micrometer and for determining its position.

Another object is the provision of improved control means for actuating, and determining the actuation of, a micrometer.

Another object is the provision of means for obtaining a fast and accurate reading of a micrometer in the measurement of objects.

Another object is the provision for obtaining precision, speed and ease of operation in the use of a micrometer.

Other objects and a fuller understanding of the invention may be had by referring to the following description and claims, taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a plan view of apparatus embodying my invention, with portions cut away for purposes of illustration;

FIGURE 2 is a side view of the apparatus shown in FIGURE 1 and looking in the direction of the arrows 2-2 of FIGURE 1;

FIGURE 3 is an end view of the apparatus shown in FIGURE 1 and looking in the direction of the arrows 33 of FIGURE 1;

FIGURE 4 is an end view of the apparatus shown in .FIGURE 1 and looking in the direction of the arrows connections is also mounted upon the base 11. A supply 3,190,009 Patented June 22, 1965 cable 14 connected to a suitable source of electric current is connected to the control box 13. A cable 15 carries the current from the control box 13 to the motor 12. Other wires 16, 17, 18, 19 and 72 enter the control box 13 and are interconnected with the wires through the cable 15 so as to contribute to the control of the operation of the motor 12.

The rotor of the motor 12 has extending therefrom in axial alignment therewith a shaft 22. This rotor shaft 22 is coupled by a coupling 23 with a shaft 24 which is journaled in a bearing assembly 25 carried by a support 26. A cover 49 secured by bolts 50 covers and guards the bearing assembly 25. This support 26 is secured to and is carried by the base 11.

Keyed to the shaft 24 so as to rotate therewith is a cogged or toothed pulley 27. Coupled to the shaft 24 by a coupling 28 is a shaft 29 of a mechanical counter mechanism 30. It is noted that the shafts 22, 24 and 29 are interconnected in axial alignment. The counter mechanism 30, as shown, is a mechanical counter, such as for example, a Veeder-Root counter. It may, however, be another mechanical counter or it may be an electronic counting or computing device which measures and indicates the rotative progression of the shaft of the counter and hence the rotative progression of the shafts 22 and 24. The mechanism of the counter 30 is such that the number of rotations of the shaft 29 and of the shafts 22 and 24 coupled therewith, is determined and indicated relative to a reference. If the counter is first set at zero, then the reference is zero and the counter will indicate the number of rotations that have occurred after the setting of the counter at zero.

A switch mechanism 71 is mounted by a bracket 73 to the counter 30. Arriving at a predetermined and preset number of rotations, the switch mechanism 71 is actuated. By the wires 72 leading from the switch mechanism 71 to the control box 13, the motor 12 thus may be tie-energized automatically after the completion of the predetermined number of rotations and hence when the rotational progress of the motor rotor has reached a certain preselected point. The cut-off of the current to the motor by the switch mechanism 71 is obtained through the control box 13 interconnecting both the motor 12 and the switch mechanism 71.

A micrometer, denoted generally by the reference character 57, is carried by a support 62 connected to and extending up from the base 11. A bolt 63 clamps a nonrotatable portion 59 of the micrometer 57 firmly in fixed position. A rotatable barrel or head 58 revolves around the non-rotatable portion 59in the well-known manner so as to extend or retract the spindle or finger 64 of the micrometer longitudinally of the axis of the micrometer. As is Well known, rotation of the barrel 58 causes the axial extension and retraction of the spindle or finger 64 which is adapted to measure parts or workpieces, such as the workpiece 65.

A coarse scale 60 marked on the non-rotatable part 59 and a Vernier or fine scale 61 is marked on the rotatable barrel 58 and with these scales a reading of the position or degree of extension of the spindle 64 may be determined and indicated.

To position and hold a part or workpiece to be measured, such as workpiece 65, a back-up member 66 is adjustably mounted to the base 11 by bolts extending through openings in the base 11 and through slots 69 in the horizontal portion 68 of the back-up member 66. A vertical portion 67 extending at right angles to the horizontal portion 68 provides a backing for the workpiece 65. The surface of the vertical portion 67 engaged by the workpiece 65 is a reference against which the Workpiece 65 is measured by the extension of the spindle 64. By loosening the bolts 70 and sliding the back-up member 66 relative to the base 11, the position of the back-up member 66 may be adjusted.

Non-rotatively secured to the rotatable barrel 58 by means of a screw bolt 56 is an adapter head 55. By having non-circular interengaging portions on the bolt 56 and barrel 58, the adapter head 55 is non-rotatively secured to the barrel 58 so as to rotate therewith. As seen in the drawings, the adapter head 55 has a rim portion which extends out radially beyond the radial extent of the barrel 5 8. The opposite sides of the rim of the adapter head 55 are chamfered and inclined toward each other. These chamfered opposite sides provide camming surfaces on the head 55.

Secured to a bracket 31 mounted on the base 11 are two microswitches and 21. Micro-switch 20 has a contact finger 20A biased to resiliently extend outwardly therefrom toward the axis of the micrometer. Also micro-switch 21 has a contact finger 21A biased to extend outwardly therefrom toward the axis of the micrometer. These fingers 20A and 21A are spaced apart longitudinally of the micrometer. They are resiliently biased to extend into the path of the rim portion of the adapted head 55. Upon the contact fingers 26A and 21A engaging an inclined camming surface of the head 55 and riding up thereon to the maximum circumference of the rim, the corresponding micro-switch is actuated to open up and disconnect the flow of current therethrough. When the head 55 moves in one longitudinal direction, it is engaged at one limit of its range by finger 20A and at the other limit of its range by finger 21A. Thus microswitches 20 and 21 are limit switches which control the flow of current in correspondence with the travel of the head 55 longitudinally of the axis of the micrometer.

Switch 20 has Wires 16 and 17 which lead to the control box 13 and switch 21 has wires 18 and 19 which lead to the control box 13. By the interconnections in the control box 13, the motor 12 is de-energized upon the rim portion of the adapter head 55 engaging and depressing either the contact finger 20A or the contact finger 21A.

Extending from the adapter head 55 on diametrically opposite sides are two pins or rods 54. These pins or rods 54 are parallel to each other and to the axis of the micrometer 57. The rods or pins 54 extend in a sliding fit through annular bushings 53 which are carried at the opposite ends of a rotatable crossarm 52. The interengagement ofthe pins 54 in the bushings 53 on the arm 52 is such that rotation of the arm 52 rotates the head 55 and hence the barrel 58, and at the same time permits the head 55 and barrel'58 to move in an axial direction toward and away from the arm 52. Therefore rotative motion may be applied to the barrel 58 and at the same time permit its axial movement by reason of the screw mechanism within the micrometer 57 operating in the usual manner of such micrometers.

The crossarm 52 is non-rotatively secured to the end of a shaft 44 which is journaled in a bearing assembly denoted generally by the reference character 45. This bearing assembly 45 is carried by a support 46 which is secured to and extends upwardly from the base 11. Keyed or non-rotatively secured to the opposite end of the shaft 44 is a cogged or toothed pulley 36. Rotation of the pulley 36 rotates the arm 52 through the shaft 44 and the arm 52, in turn, rotates the rotatable head 55 and barrel 58 of the micrometer while permitting relative axial movement between the rotatable part and the non-rotatable part of the micrometer. A cover 47 secured by bolts 48 covers and guards the bearing assembly 45.

The supports 2-6 and 46 are disposed in substantially the same plane and there is a space provided therebetween. In this space there is positioned a block 39 which is in a sliding fit so as to move vertically up and down between the guides provided by the supports 26 and 46. As seen in FIGURE 1, portions of the supports 26 and 46 are cut away to leave shoulders against which the block 39 abuts. A clamping bar 4]. extends across the space between the supports 26 and 46 so as to engage the oppositely disposed shoulders provided on these supports 26 and 4%. As better seen in FIGURE 5, a bolt 42 threadably engaged with clamping bar 41, upon being tightened, clamps the bar 41 against the supports 26 and 46 and hence locks the block 39 in fixed position relative to the supports 26 and 46. In this manner, the elevation of the block 3 may be adjusted and determinably fixed.

A shaft 37 is journaled in a bearing assembly denoted generally by the reference character 38 which is carried by the block 39. A cover 40 secured by bolts 43 covers and guards the bearing assembly 38. The axes of the shafts 37, 24 and 44 are parallel to each other; also a vertical plane through the axis of the shaft 37 is equidistant from the axes of shafts 24 and 44. The elevation of the axis of shaft 37 relative to a horizontal plane passing through the axes of shafts 24 and 44 depends upon the elevation of the block 39 relative to the supports 26 and 46.

Keyed or non-rotatively secured to the shaft 37 is a cogged or toothed pulley 33. Also keyed or non-rotatively secured to the shaft 37 is another cogged or toothed pulley 34.

Reeved around the pulleys 34 and 36 is a cogged or toothed belt 35 of suitable resilient material. Reeved around the pulleys 27 and 33 is another cogged or toothed belt 32 of suitable resilient material. The belts 32 and 35 have teeth protruding from a side thereof so as to intermesh with the teeth of the cogged pulleys about which they are reeved. The pulley belts may be made of a suitable rubber-like material which flexes enough to bend around the pulleys but which do not stretch so as not to permit play or lag in the driving connection between the pulleys by means of the belts. By reason of the intermeshing of the teeth provided on the belts and pulleys, there is no slippage and a positive drive mechanism is provided between the shaft 24 and the shaft 44 by means of the four pulleys and two belts.

It is noted that the diameter of pulley 33 is larger than the diameter of pulley 27, and the diameter of pulley 36 is larger than the diameter of pulley 34. Also, the diameter of pulley 33 is larger than the diameter of pulley 34. In the illustration of apparatus given by way of example in the drawings, the drive ratio provided by the relative sizes of the pulleys is such that the shaft 37 rotates one time while the shaft 24 rotates five times. In other words, there is a five-to-one ratio provided. Also by reason of the ratio in the sizes of the pulleys 36 and 34, the shaft 44 rotates one time while the shaft 37 rotates five times. Thus by a combination of ratios in the sizes of the four pulleys, the shaft 44 rotates 25 times while the shaft 24 rotates one time. Thus the speed of rotation of the shaft 24 is 25 times the speed of the shaft 44. In this matter, while the rotor shaft 22 rotates 25 times, the barrel 58 of the micrometer 57 rotates on its axis one time. There is thus a fixed ratio between the speed of the motor 12 and the rotation of the micrometer barrel or head and this ratio is such that the micrometer barrel or head is rotated at a slower speed than the speed of rotation of the motor rotor.

In the example illustrated, when the micrometer 57 indicates a one-inch thickness to the workpiece 65, the counter 3% also indicates a one-inch thickness. By reason of the fact that the counter 38 indicates rotational progress to a unit of one ten-thousandths of an inch (.0001), a fine degree of reading of the rotational progress is obtainable. When the micrometer is measuring a half inch, then the reading on the counter will indicate .5000 of an inch. A quick and ready reading of the position of the micrometer barrel or head is obtained by reading the indication on the dial of the counter 30.

The micrometer may be readily driven into position by turning the control knob 13A on the electric control box 13. A rheostat in the control box 13 permits the adjustment of the speed of the motor. Also the manipulation of switches 13B and 13C of the control box 13 determines the direction of rotation of the reversible motor 12. Thus the micrometer may be power-driven to rotate in either direction and at a desired speed. Overdriving of the micrometer beyond axial spaced limits is prevented bythe limit switches 20 and 21 which, through wires 16, 17, 18 and 19 leading to the control box 13, de-energize the motor 12 when the micrometer has driven beyond the predetermined limits. Also by means of the switch mechanism 71 on the counter 30, the motor 12 may be automatically de-energized upon rotation beyond a preselected position.

As will be apparent, this apparatus provides for fast and ready measuring of workpieces with a micrometer. The micrometer is easily and speedily operated and the reading of the measured amount is quick and easily determined to a fine and precise degree by observing the dial on the counter. As there is a proportional amount of rotation of the micrometer head relative to the rotations of the motor rotor, the rotational progress indicated by the counter 30 reflects or indicates a proportional rotational progression of the head or barrel of the micrometer. A fine and precise reading of the micrometer is thus readily obtained.

The present disclosure includes that contained in the appended claims, as well as that of the foregoing description.

Although this invention has been described in its preferred form with a certain degree of particularly, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and scope of the invention as hereinafter claimed.

What is claimed is:

1. Mechanism for operating a rotatable micrometer head comprising in combination, a support, mounting means carried by the support for mounting the micrometer head for rotation relative to a first reference position, an electric motor carried by the said support, a driving shaft rotatable by said motor, a counter having an actuating shaft extending therefrom, connecting means operatively connecting said driving shaft and said actuating shaft for actuating the counter in direct correspondence with the rotation of the driving shaft to indicate the rotational progress of said driving shaft from a second reference position, a driven rotational member, coupling means coupling said micrometer head and said driven rotational member to permit axial movement of the micrometer head relative to said driven rotational member and to rotate the micrometer head in accordance with the rotation of said driven rotational member, switch mechanism operable by movement of the counter for controlling the energization of the said motor in accordance with a preset number of rotations of the counter, and power-transmitting means operatively connecting said driving shaft and said driven rotational member to drive the driven rotational member upon rotation of said driving shaft by said motor, said power-transmitting means including fixedratio reduction means to cause rotation of the driven rorational member at a slower rate of speed than the rotation of said driving shaft whereby the rotational progress of the driving shaft indicated by said counter corresponds with a proportional rotational movement of the driven rotational member and with the position of the micrometer head coupled therewith, said connecting means being independent of said reduction means whereby the actuating shaft of the counter is directly actuated by the driving shaft.

42. The combination of a micrometer head having a rotatable part, an electric motor, a rotatable driving shaft rotated by said motor, a counter having an actuating shaft extending therefrom, connecting means operatively connecting said driving shaft and said actuating shaft for actuating the counter in direct correspondence with the rotation of the driving shaft for indicating the rotated progression of said driving shaft, switch means operable by the movement of the said counter to preset positions thereof for controlling energization of said electric motor, a rotatable driven member coupled to said rotatable part of the micrometer head for rotating the same, power-transmitting means operatively connecting said driving shaft and driven member, said power-transmitting means in cluding proportioning means for rotating the driven member at a rate of speed less than, and at a constant ratio to, the rate of speed of the said driving shaft, said connecting means being independent of said reduction means whereby the actuating shaft of the counter is directly actuated by the driving shaft, and control means including adjustable rheostat means for controlling the operation and speed of said motor, the indication of the rotated progression of said driving shaft indicated by said counter providing an indication of the rotated progression of said driven member in proportion thereto and the corresponding position of saidrotatable part of the micrometer head.

3. The combination of first rotatable means for rotating the rotatable part of a micrometer head, second rotatable means powered by an electric motor for operating a counter mechanism coupled therewith for indicating the rotated progression of said second rotatable means, switch means operable by said counter mechanism for eflfecting the operation of the said motor by the progressive movement of the counter mechanism to a reference position, power-transmitting means including speed-reducing means operatively connecting said first rotatable means and said second rotatable means for driving said first rotatable means at a fixed ratio to, and at a lesser rate than, the

' speed of the second rotatable means, whereby the rotatable progression of the second rotatable means indicated by said counter mechanism indicates the proportional and lesser rotatable progression of the first rotatable means and of the rotatable part of said micrometer head, said speed-reducing means not including said second rotatable means whereby the counter is operated directly by the second rotatable means without modification of speed by the speed-reducing means.

4. The combination of rotatable driven means coupled to the head of a micrometer for turning the same, rotatable driving means coupled to an electric motor to be rotated by said motor, power-transmitting means operatively connecting said driving means and said driven means including speed-reduction means for rotating the driven means and micrometer head coupled therewith at a speed less than and at a fixed ratio to the speed of rotation of the driving means rotated by the motor, indicating means coupled directly to the driving means to be operated there by at the speed of rotation of the driving means for indicating the rotative progression of said driving means independently of the speed of the driven means and thereby the proportional rotative progression of the micrometer head coupled to said driven means and switch means operable by said indicating means for controlling energiza tion of the electric motor in accordance with indications of said indicating means.

5. Apparatus for rotating the rotatable barrel of a micrometer and determining the progression of the rotation of said barrel, comprising in combination, a first shaft directly rotatably by an electric motor, a counter mechanism coupled with said first shaft to rotate at the same speed of rotation as the first shaft for indicating the progression of the rotation of said first shaft, a first toothed pulley connected to said first shaft to rotate therewith, a second shaft coupled to the barrel of said micrometer to rotate said barrel and to permit axial movement of said barrel during rotation, a second toothed pulley connected to said second shaft to rotate the same, a third shaft rotatable on its axis at a location spaced from the axes of the first and second drafts, a third toothed pulley and a fourth toothed pulley connected to said third shaft to rotate therewith, a first toothed pulley belt reeved about said first toothed pulley and said third toothed pulley to drivingly rotate the third toothed pulley, a second toothed pulley belt reeved about said fourth toothed pulley and said second toothed pulley to drivingly rotate the second toothed pulley, the driving ratio of said pulleys being such that said second shaft is rotated by said first shaft at a fixed ratio and at a lesser speed than said first shaft, said counter mechanism by indicating the progression of rotation of said first shaft independently of the driving of the second shaft by said pulleys and belts indicating the proportional corresponding progression of rotation of said second shaft and of the micrometer barrel coupled therewith first switch means operable by movement of the counter mechanism to preset position for controlling energization of said motor, and second switch means operable by movement of said rotatable barrel of the micrometer to limiting positions for controlling energization of said motor.

6. Apparatus for operating a micrometer having a rotatable head by power derived from an electric motor, comprising in combination, a rotatable member, pin and bushing means interconnecting said rotatable member and said head to rotate the head by the rotatable member and to permit movement of the head in an axial direction relative to said rotatable member, a driven pulley connected to said rotatable member to rotate the rotatable member, a driving pulley connected to said electric motor to be rotated thereby, a'pair of intermediate pulleys on a common axis, pulley belts operatively connecting said driving, driven and intermediate pulleys, said pulleys and belts having intermeshing teeth to avoid slippage of the belts on the pulleys, said pulleys being of relative sizes ratioed to rotate the driven pulley at a lesser speed relative to the speed of the driving pulley, indicating means operatively connected directly to said driving pulley and by-passing said belts and intermediate pulleys for indicating the progression of rotation of said driving pulley relative to a reference, said means simultaneously indicating the proportional progression of rotation of said driven pulley driven by the driving pulley through said belts and intermediate pulleys whereby the micrometer head may be operated and its rotative position determined and switch means actuated by said indicating means and by said micrometer rotatable head for controlling energization of the said motor by movements of the indicating means and the rotatable head, respectively, to reference positions.

7. Mechanism for rotating a micrometer head by an electric motor at a rate proportionably less than the speed of the rotor of the motor and for determining the rotative progression of the micrometer head through a determination of the rotative progression of the rotor of the motor, comprising in combination, power-transmitting means for transmitting power from the motor to the micrometer head to rotate the same in a direction in correspondence with the rotation of the rotor of the motor, said powertransmitting means including proportioning means for rotating the micrometer head a proportionately less amount than the rotation of the rotor of the motor, rotation-indicating means coupled directly with the rotor of the motor and by-passing said proportioning means for indicating the progression of rotation of the said rotor relative to a reference independently of the rotation of the micrometer head whereby the proportionately lesser progression of rotation of the micrometer head may be determined and switch mechanism means operable by movement of the rotation-indicating means to preset position for automatically controlling energization of the said motor, and control means in circuit arrangement with said switch mechanism means for manual control of speed and rotative direction of said rotor.

8. Mechanism as defined in claim 7 and in which said power-transmitting means includes toothed pulleys and toothed belts interengaged therewith and arranged to provide positive transmission of power at a fixed ratio of speed to provide said proportioning of rotation and including limit switch means in circuit arrangement with said control means and operable by movement of said micrometer head to set limits of movement for controlling energization of the said motor.

9. Mechanism as defined in claim 7 in which the micrometer head has pins extending therefrom parallel to the axis of the head and revolved by a rotatable member rotated by the said power-transmitting means and in which said rotation-indicating means is a counter mechanism having a shaft operatively connected to the rotor shaft to be driven in direct correspondence with the rotation of the rotor, the axis of the counter mechanism shaft being laterally spaced from the axis of the micrometer head.

10. The combination of an electric motor having a rotor, of first means for rotating by power derived from the rotor of the electric motor the rotatable head of a micrometer to rotate the same in correspondence with the direction of rotation of the motor rotor, said first means including pin means carried by the micrometer head and extending parallel to and at a distance from the axis thereof for rotating the said head by revolving the pin means about said axis, second means driven by said first means for proportioning the rotation of the said head at a fixed ratio to the speed of the motor rotor, and third means driven by said motor rotor for counting the rota tional progress of the motor rotor, said third means being operated independently of said second means to provide a direct count uneffected by rotation of said head by the first means, the count given by the third means giving an indication of the proportional amount of rotation of said head.

11. The combination of a rotatable micrometer barrel movable along its axis as it is rotated, an adapter head connected therewith to rotate and move axially with said barrel, said adapter head having a rim portion extending therearound, said rim portion having chamfered camming surfaces on opposite sides thereof inclined toward each other, an electric motor, control mechanism for controlling the supply of current to said motor for governing the speed and direction of the operation of the same, power-transmitting mean-s operatively connecting the rotor of said motor and said adapter head for rotating the micrometer barrel, said power transmitting means including pin-and-socket means associated with the micrometer barrel for permitting axial movement of the barrel upon revolving the pin-and-socket means about the axis of the said barrel, and limit switch means including contact fingers positioned relative to said adapter head to be actuated by movement of said camming surfaces in an axial direction relative to the contact fingers of said limit switch means to actuate the limit switch means at the limits determined by the spacing of said contact fingers, said limit switch means operating said control mechanism to stop the supply of current to said motor upon said rim portion traveling to either of the said limits.

12. The combination as defined in claim 11 and including in said power-transmitting means speed reduction means to rotate the adapter head at a fixed ratio to the rotation of the motor rotor and at lesser speed, and including counting means coupled directly to the motor rotor and not through said speed-reduction means for counting at the greater speed of the rotor the rotation of the motor rotor, and switch mechanism operable by said 9 counting means for controlling energization of said motor 2,397,312 in accordance with a presettable condition of the counting 2,624,121 means. 2,624,122 2,674,896 References Cited by the Examiner 5 2 54 75 5 UNITED STATES PATENTS 1,172,793 2/16 Hapgood 235-103 2,160,024 5/39 Marcellus 33-132 2,344,508 3/44 Groll 33-132 10 Forrest 74-216 5 Knobel 33-164 Knobel 33-164 Arones 7-231 Knobel 33-164 X Hanes 33-126.75 Gunther 33-164 ISAAC LISANN, Primary Examiner. 

1. MECHANISM FOR OPERATING A ROTATABLE MICROMETER HEAD COMPRISING IN COMBINATION, A SUPPORT, MOUNTING MEANS CARRIED BY THE SUPPORT FOR MOUNTING THE MICROMETER HEAD FOR ROTATION RELATIVE TO A FIRST REFERENCE POSITION, AN ELCTRIC MOTOR CARRIED BY THE SAID SUPPORT, A DRIVING SHAFT ROTATABLE BY SAID MOTOR, A COUNTER HAVING AN ACTUATING SHAFT EXTENDING THEREFROM, CONNECTING MEANS OPERATIVELY CONNECTING SAID DRIVING SHAFT AND SAID ACTUATING SHAFT FOR ACTUATING THE COUNTER IN DIRECT CORRESPONDENCE WITH THE ROTATION OF THE DRIVING SHAFT TO INDICATE THE ROTATIONAL PROGRESS OF SAID DRIVING SHAFT FROM A SECOND REFERENCE POSITION, A DRIVEN ROTATIONAL MEMBER, COUPLING MEANS COUPLING SAID MICROMETER HEAD AND SAID DRIVEN ROTATIONAL MEMBER TO PERMIT AXIAL MOVEMENT OF THE MICROMETER HEAD RELATIVE TO SAID DRIVEN ROTATIONAL MEMBER AND TO ROTATE THE MICROMETER HEAD IN ACCORDANCE WITH THE ROTATION OF SAID DRIVEN ROTATIONAL MEMBER, SWITCH MECHANISM OPERABLE BY MOVEMENT OF THE COUNTER FOR CONTROLLING THE ENERGIZATION OF THE SAID MOTOR IN ACCORDANCE WITH A PRESET NUMBER OF ROTATIONS OF THE COUNTER, AND POWER-TRANSMITTING MEANS OPERATIVELY CONNECTING SAID DRIVING SHAFT AND SAID DRIVEN ROTATIONAL MEMBER TO DRIVE THE DRIVEN ROTATIONAL MEMBER UPON ROTATION OF SAID DRIVING SHAFT BY SAID MOTOR, SAID POWER-TRANSMITTING MEANS INCLUDING FIXEDRATIO REDUCTION MEANS TO CAUSE ROTATION OF THE DRIVEN ROTATIONAL MEMBER AT A SLOWER RATE OF SPEED THAN THE ROTATION OF SAID DRIVING SHAFT WHEREBY THE ROTATIONAL PROGRESS OF THE DRIVING SHAFT INDICATED BY SAID COUNTER CORRESPONDS WITH A PROPORTIONAL ROTATIONAL MOVEMENT OF THE DRIVEN ROTATIONAL MEMBER AND WITH THE POSITION OF THE MICROMETER HEAD COUPLED THEREWITH, SAID CONNECTING MEANS BEING INDEPENDENT OF SAID REDUCTION MEANS WHEREBY THE ACTUATING SHAFT OF THE COUNTER IS DIRECTLY ACTUATED BY THE DRIVING SHAFT. 